Quantitative Phase Imaging via Absorption Gradient Correction
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Solution Overview
Problem
Conventional phase contrast X-ray imaging methods using coded aperture X-ray phase contrast imaging (CAXPCI) do not produce quantitative phase images, as the image contrast is a combination of phase shift due to the real part and absorption due to the imaginary part of the refractive index, rather than solely the phase shift.
Innovation Solution
Adapting the CAXPCI method to produce true phase images by calculating the gradient of the absorption function and adding a correction term to each output pixel, allowing for a linear approximation of the absorption function to isolate the phase shift, thereby achieving a more precise quantitative phase image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CAXPCI method is used to achieve short acquisition times, then productivity is improved, but measurement precision deteriorates because the images produced do not have intensities proportional only to the phase shift
Solution Approach 1:
The invention extracts the absorption component from the phase contrast image by calculating the gradient of the absorption function. This separates the harmful absorption effect from the desired phase shift measurement, allowing quantitative phase imaging to be achieved while maintaining the fast acquisition characteristics of CAXPCI.
Solution Approach 2:
The invention introduces an intermediary calculation step involving the gradient of the absorption function. This intermediary term serves as a correction that mediates between the raw phase contrast image and the desired quantitative phase image, enabling accurate phase measurement without requiring slower conventional methods.
2Measurement precision
If correction terms are added to image processing algorithms to improve measurement precision, then quantitative phase imaging accuracy is improved, but device complexity increases
Solution Approach 1:
The invention changes the parameter being measured by focusing on the gradient of the absorption function rather than the absolute absorption values. This parameter transformation simplifies the correction process and reduces computational complexity while maintaining measurement precision.
Solution Approach 2:
The invention replaces complex mechanical or hardware-based solutions with a mathematical substitution approach. By using gradient calculations and linear approximations, the invention achieves accurate quantitative phase imaging through computational methods rather than more complex physical measurement systems.
3Device complexity
If linear approximation of absorption function is used to simplify processing, then device complexity is reduced, but measurement precision deteriorates when absorption is not uniform
Solution Approach 1:
The invention incorporates feedback by using the calculated absorption gradient to correct the phase image. This feedback mechanism allows the system to automatically compensate for non-uniform absorption conditions, maintaining measurement precision while keeping the processing approach simple and robust.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method is robust and provides accurate quantitative phase images, even when absorption is not uniform, reducing complexity and artifacts in image processing, and can be applied over a wide range of situations.
Implementation Method 1
providing a source of X-rays
Implementation Method 2
the term responsible for phase changes (the difference from unity of the real part of the refractive index) is typically of the order of 1000 times larger than the part responsible for absorption
Implementation Method 3
Conventional X-ray imaging systems are based on absorption of X-rays
Implementation Method 4
directing the source of X-rays to define at least one X-ray beam with opposed first and second edges
Implementation Method 5
A recent proposal, in WO 2008/029107, proposes carrying out phase-contrast imaging using a method that can work with conventional X-ray sources. In this approach, typically a pair of masks are used, one between the detector and the sample to create one or more X-ray beams
Data Source
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AI summary
A method of phase imaging uses X-ray beams having edges overlapping with pixels. A phase image may be obtained from first and second images using one or more X-ray beam, the first image being measured with the first edge but not the second edge of each X-ray beam overlapping the corresponding pixel(s) and the second image being measured with the second edge but not the first edge overlapping the corresponding pixel(s). The gradient of the X- ray absorption function may be calculated and a proportional term included in the image processing to calculate a quantitative phase image.